Linq到具有多级子引用的实体查询

Question

I have been having too much trouble designing a query to retrieve questions that a candidate have already attempted and another query for the questions that a candidate has not attempted. This is for a examination/test/form/survey type application.

The scenario is a candidate(OAS_UserDetail) is associated with many groups(OAS_Group). One group can have many tests. A test can have many questions. A question can have many options.

When a candidate attempts a question it is stored in table TestResponse having reference to the session, (the answerSelected in table TestResponse is actually the QuestionOption.Id). I believe TestSession can act as a bridge for TestResponse to get the details of user, test and group.

This seems to me a good but somewhat complex design for me as far as querying is concerned through Linq. Below is what I tried to do and got stuck and end up writing Linq in method syntax instead of query syntax.

OAS.DataModels.OAS_Question questionsAttempted = 
            from q in db.OAS_Questions
            where q.OAS_Test.OAS_Group.Candidates.Contains(
                      db.OAS_UserDetails.Single(u => u.UserName == HttpContext.User.Identity.Name)
            )                         
            select q;

Answer 1

Linq query syntax is very similar to SQL. You should be able to do what you need using "join" operators.

Here's a good overview:

http://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b

Answer 2

So you are looking for questions of a candidate of which the options either are or aren't in the candidate's TestResponse records. I think this could work:

(from u in OAS_UserDetail
from g in u.OAS_Group
from t in g.OAS_Test
from q in t.OAS_Question
from o in q.OAS_QuestionOption
where u.Id == userId // a variable
where u.OAS_TestSession
      .SelectMany(s => s.OAS_TestResponse)
      .Select(r => r.AnswerSelectedId).Contains(o.Id)
select q).Distinct()

and for the questions that the candidate did not attempt: where !u.OAS_TestSession...